In many display applications, including television and alphanumeric displays, it is desirable to have mounted on a thin panel a matrix of discrete, closely-spaced radiation-emitting elements which can be individually controlled over a wide brightness range.
Commercial television and some alphanumeric displays presently rely on the bulky cathode ray tube to control luminescent elements on a display screen. Good brightness range is achieved, and few connection leads are required, but the size of the tube is a drawback for many applications.
Various thin panel display devices have been proposed, but these have generally relied on row and column addressing and thus have required as many as 1040 external connections for controlling a 520 by 520 element display. For example, Luo et al. U.S. Pat. No. 4,042,854 shows an AC-driven electroluminescent display with leads for each row and column and a pair of thin-film transistors and a capacitor at each display element.
When electroluminescent devices are used as the radiation-emitting elements, increased brightness is generally desired, and it is also desirable to produce satisfactorily bright luminescence with the same level DC voltages as are commonly used in CMOS logic devices (approximately 15 volts DC), thereby eliminating the additional cost of converting logic output signals to higher voltages for producing luminescence. A difficulty with conventional electroluminescent devices is that, when a sandwich construction (two area electrodes on either side of a luminescent layer) is used, the transparent electrode placed between the transparent substrate and the luminescent film, by virtue of its thinness and high resistance, contributes to detrimental capacitance effects which limit operating speed and frequency. It would thus be desirable to have an electroluminescent display element with sufficiently thick electrodes all on one side of the luminescent layer.
Several references have shown electroluminescent devices that employ transversely-spaced electrodes on one side of a luminescent layer. Kanie U.S. Pat. No. 3,519,871 and Mash U.S. Pat. No. 2,928,974 show the electrodes positioned opposite the viewing side of the luminescent layer. Kanie suggests direct-current operation and shows a vacuum-deposited luminescent layer. Robinson U.S. Pat. No. 3,312,825 shows AC-sensitive, semiconductive luminescent material filling wide gaps between transversely spaced electrodes. Mager et al. U.S. Pat. No. 2,684,450 shows an AC-sensitive layer composed of a dielectric base material filled with small phosphor particles covering the electrodes. Vecht U.S. Pat. No. 3,731,353 shows a DC-sensitive device that produces luminescence only along narrow zones.
Vlasenko et al. U.S. Pat. No. 3,889,016 shows a method for producing a DC-sensitive electroluminescent film by vacuum deposition.